Interaction between bradykinin and voltage-sensitive sodium channels in myelinated nerve fibers

Summary The effects of externally and internally applied bradykinin on the excitability of single myelinated nerve fibers were studied. External bradykinin (10 M) slightly prolongs the action potential of a single myelinated nerve fiber; hence, when the fibers are stimulated by long-lasting pulses, this raises the frequency of repetitive firing in sensory fibers and evokes repetitive activity in motor fibers. Under voltage-clamp conditions, sodium channel inactivation is slowed, while sodium channel activation remains unaffected. Prolonged depolarization of th membrane leads to a maintained sodium current. The voltage dependence of the steady-state sodium current inactivation (h ) is shifted in the depolarized direction by 10 mV. Internally applied bradykinin produces a frequency-dependent block of the sodium current. The phenomena described here imply that more than one site on the sodium channel is modified by bradykinin.     

Interaction between bradykinin and voltage-sensitive sodium channels in myelinated nerve fibers

The effects of externally and internally applied bradykinin on the excitability of single myelinated nerve fibers were studied. External bradykinin (10 microM) slightly prolongs the action potential of a single myelinated nerve fiber; hence, when the fibers are stimulated by long-lasting pulses, this raises the frequency of repetitive firing in sensory fibers and evokes repetitive activity in motor fibers. Under voltage-clamp conditions, sodium channel inactivation is slowed, while sodium channel activation remains unaffected. Prolonged depolarization of the membrane leads to a maintained sodium current. The voltage dependence of the steady-state sodium current inactivation (h infinity) is shifted in the depolarized direction by approximately 10 mV. Internally applied bradykinin produces a frequency-dependent block of the sodium current. The phenomena described here imply that more than one site on the sodium channel is modified by bradykinin.     

Variation in the number and size of myelinated nerve fibers regenerated after repeated localized freezing of the sciatic nerve of rats]

The number and size of myelinated fibres have been determined in the nerve to medial head of the gastrocnemius muscle of Rats in which the sciatic nerve had been frozen locally 1 to 5 times at monthly intervals. The contralateral nerve was used as a control. When the measurements were made one month after the last freezing, the number of fibres increased progressively until the 3rd freezing, reaching about 220% of the normal value. No higher values were observed after 4 or 5 freezings. The mean diameter of fibres decreased with the number of operations. When the measurements were made 3, 6, 12 or 18 months after the 3rd freezing, the number of fibres decreased by about 30% between the 1st and the 3rd month and then stabilized. The mean diameter of fibres increased progressively. However, at the 18th month, the size of the myelinated fibres had not reached the normal value.     

Potassium inactivation in myelinated nerve fibres

Zusammenfassung Die Inaktivierung der K-Permeabilität wurde in Voltage-clamp-Experimenten an markhaltigen Nervenfasern untersucht. Bei langdauernden Depolarisationen fällt der K-Strom annähernd exponentiell auf einen stationären Endwert ab. In Richtung Depolarisation nehmen die Zeitkonstanten dieser Abnahme zu; sie sind um mehrere Grössendornungen grösser als die übrigen Zeitkonstanten. Die Inaktivierungskurve ist s-förmig und bleibt selbst bei grösseren Depolarisationen auf einem endlichen Wert.     

Water compartments in the myelinated nerve. III. Pulsed NMR results.

3 experimentally distinct transverse relaxation components of the water in frog sciatic nerve are obtained by Carr-Purcell-Meiboom-Gill technique. The relative weights of these components: approximately 29%; approximately 50%; approximately 21% fit well with water compartments in this tissue as revealed by previous methods.     

Water compartments in the myelinated nerve. III. Pulsed NMR result

Summary 3 experimentally distinct transverse relaxation components of the water in frog sciatic nerve are obtained by Carr-Purcell-Meiboom-Gill technique. The relative weights of these components: 29%; 50%; 21% fit well with water compartments in this tissue as revealed by previous methods.The previous communication in this series: V. Vasilescu, D.-G. Mârgineanu and Eva Katona, Experientia33, 192 (1977).     

An analysis of the distribution of the myelinated nerve fibers in the optic fascicle of a beagle dog

The composition of both optic fascicles of a Beagle dog was studied in topographically oriented, semithin transections of whole nerve stained with toluidine blue. About 165,000 myelinated fibers were present in each nerve, their maximum caliber reaching 11 micron; large, less densely arranged fibers occurred especially in the dorso-temporal region.     

An analysis of the distribution of the myelinated nerve fibers in the optic fascicle of a Beagle dog

Summary The composition of both optic fascicles of a Beagle dog was studied in topographically oriented, semithin transections of whole nerve stained with toluidine blue. About 165,000 myelinated fibers were present in each nerve, their maximum caliber reaching 11 m; large, less densely arranged fibers occurred especially in the dorso-temporal region.We are grateful to Dr D.C. Naylor, Mrs K. Schnider, Mr F. da Silva and Mr K. Traber for their aid.     

Fluctuations in excitability of single myelinated nerve fibres

Résumé Il est possible de montrer des fluctuations aléatoires de l'excitabilité électrique de fibres nerveuses myélinisées isolées excitées au moyen de chocs proches du seuil. L'amplitude de cette fluctuation a été comparée pour des excitants rectangulaires de deux durées (0,1 et 10 msec); elle est plus grande quand on utilise des chocs brefs. Ces résultats suggèrent que les composantes de relativement haute fréquence du spectre de la fluctuation sont importantes.